Plasmid DNA Prime/Protein Boost Vaccination against Campylobacter jejuni in Broilers: Impact of Vaccine Candidates on Immune Responses and Gut Microbiota.

Campylobacter infections, traced to poultry products, are major bacterial foodborne zoonoses, and vaccination is a potential solution to reduce these infections. In a previous experimental trial using a plasmid DNA prime/recombinant protein boost vaccine regimen, two vaccine candidates (YP437 and YP9817) induced a partially protective immune response against Campylobacter in broilers, and an impact of the protein batch on vaccine efficacy was suspected. This new study was designed to evaluate different batches of the previously studied recombinant proteins (called YP437A, YP437P and YP9817P) and to enhance the immune responses and gut microbiota studies after a C. jejuni challenge. Throughout the 42-day trial in broilers, caecal Campylobacter load, specific antibodies in serum and bile, the relative expression of cytokines and ß-defensins, and caecal microbiota were assessed. Despite there being no significant reduction in Campylobacter in the caecum of vaccinated groups, specific antibodies were detected in serum and bile, particularly for YP437A and YP9817P, whereas the production of cytokines and ß-defensins was not significant. The immune responses differed according to the batch. A slight change in microbiota was demonstrated in response to vaccination against Campylobacter. The vaccine composition and/or regimen must be further optimised.

Evaluation of Two Recombinant Protein-Based Vaccine Regimens against Campylobacter jejuni: Impact on Protection, Humoral Immune Responses and Gut Microbiota in Broilers.

Campylobacter infections in humans are traced mainly to poultry products. While vaccinating poultry against Campylobacter could reduce the incidence of human infections, no vaccine is yet available on the market. In our previous study using a plasmid DNA prime/recombinant protein boost vaccine regimen, vaccine candidate YP437 induced partial protective immune responses against Campylobacter in broilers. In order to optimise vaccine efficacy, the vaccination protocol was modified using a protein prime/protein boost regimen with a different number of boosters. Broilers were given two or four intramuscular protein vaccinations (with the YP437 vaccine antigen) before an oral challenge by C. jejuni during a 42-day trial. The caecal Campylobacter load, specific systemic and mucosal antibody levels and caecal microbiota in the vaccinated groups were compared with their respective placebo groups and a challenge group (Campylobacter infection only). Specific humoral immune responses were induced, but no reduction in Campylobacter caecal load was observed in any of the groups (p > 0.05). Microbiota beta diversity analysis revealed that the bacterial composition of the groups was significantly different (p ≤ 0.001), but that vaccination did not alter the relative abundance of the main bacterial taxa residing in the caeca. The candidate vaccine was ineffective in inducing a humoral immune response and therefore did not provide protection against Campylobacter spp. infection in broilers. More studies are required to find new candidates.

Research Note: Analysis of immune responses in broilers after vaccination against Campylobacter jejuni.

Campylobacter infections traced mainly to poultry products are major bacterial foodborne zoonoses. Among the many control strategies evaluated at primary poultry level to reduce these infections, vaccination could be a solution, but no effective vaccines are available to date. A better understanding of the immune mechanisms involved in protection against Campylobacter would be helpful for designing novel vaccine strategies. The present study was designed to analyze in more depth the immune responses developed in broilers in order to potentially identify which immune parameters may be important for establishing protection against Campylobacter by comparing the immune responses obtained here with those obtained in a previous study performed on vaccinated specific-pathogen-free Leghorn chickens that presented a partial reduction of Campylobacter after experimental challenge. The protection against Campylobacter colonization was evaluated at different time points over 40 d of rearing, by measuring specific IgY levels in serum and IgA antibodies in bile reflecting the systemic and mucosal humoral responses respectively and the relative expressions of 9 cecal immune marker genes (cytokines and antimicrobial peptides), which reflect the innate and cellular immune responses. Despite no reduction of Campylobacter in the cecum, a systemic immune response over time characterized by the production of specific anti-flagellin IgY was observed, in addition to upregulation of the antimicrobial peptide avian ß-defensin (AvBD) 12 gene expression in the cecum of vaccinated broilers compared with the placebo group. However, the levels of specific anti-flagellin mucosal IgA antibodies in the bile as well as the relative expression of other cecal cytokines studied was underexpressed in the vaccinated group or similar in both groups.

Impact of DNA Prime/Protein Boost Vaccination against Campylobacter jejuni on Immune Responses and Gut Microbiota in Chickens.

Campylobacteriosis is reported to be the leading zoonosis in Europe, and poultry is the main reservoir of Campylobacter. Despite all the efforts made, there is still no efficient vaccine to fight this bacterium directly in poultry. Recent studies have reported interactions between the chicken immune system and gut microbiota in response to Campylobacter colonisation. The present study was designed to analyse in more depth the immune responses and caecal microbiota following vaccination with a DNA prime/protein boost flagellin-based vaccine that induces some protection in specific-pathogen-free White Leghorn chickens, as shown previously. These data may help to improve future vaccination protocols against Campylobacter in poultry. Here a vaccinated and a placebo group were challenged by C. jejuni at the age of 19 days. A partial reduction in Campylobacter loads was observed in the vaccinated group. This was accompanied by the production of specific systemic and mucosal antibodies. Transient relatively higher levels of Interleukin-10 and antimicrobial peptide avian ß-defensin 10 gene expressions were observed in the vaccinated and placebo groups respectively. The analysis of caecal microbiota revealed the vaccination's impact on its structure and composition. Specifically, levels of operational taxonomic units classified as Ruminococcaceae and Bacillaceae increased on day 40.